This invention relates to an apparatus for removing substances which become attached to the inner walls of a vessel, e.g., a dryer. The removal of such substances is achieved by means of scrapers.
The prior art teaches a number of different dryer structures which are utilized in industry for the drying of various materials. The construction of these dryers depends on the particular type of material to be dried therein. The drying of smeary materials, i.e., nonpourable materials, presents unusual problems.
One prior art arrangement disclosed in U.S. Pat. No. 4,245,399 provides a dryer having resilient scrapers arranged on an agitator shaft to function both as scrapers and agitating aids. The agitator shaft scrapers are arranged (1) as a spiral-shaped screw, and (2) as a vertically extending blade.
The conventional prior art devices however, have the disadvantage that a desired spacing, with respect to the wall, of less than 5 mm is very difficult to achieve, especially in the case when the dryer is a very large vessel. As a consequence, a layer of material eventually builds up on the walls due to the inability to scrape it off, and inhibits the heat transfer required for drying the rest of the material in the dryer. In the case of larger layer thicknesses this also leads to a large thermal load on the materials lying on the heated wall.